If this is CSI: Te Puke, then the crime scene is at the corner of Mark and Te Matai Rds. It was here in late 2010 that Psa, forecast to cost the kiwifruit industry $885 million, was first discovered, on an orchard known as Olympus.

Straight across the road is a factory belonging to Kiwi Pollen, which in 2009 imported 4.5kg of anthers, the pollen-bearing part of a flower's stamen, from China.

The Ministry of Primary Industries, (MPI) the successor department to the Ministry of Agriculture and Forestry (MAF), says the 2009 shipment is one of a number of potential "pathways".

Observers say it is unlikely MPI would ever admit that the shipment was the source of Psa, because MAF's fingerprints are all over that shipment - it allowed it in without any restrictions or quarantine requirements - and if that was the "pathway" it could open the department up to a huge compensation bill.

But consider the evidence: The anthers came from Shaanxi province, where Psa is endemic.

DNA testing by Otago University has confirmed that New Zealand's strain of the disease is identical to the Shaanxi one.

The 4.5kg of anthers were packed in 5kg of ice to keep them chilled, which scientists say could have kept the Psa disease alive.

Kiwi Pollen tried to extract pollen from the anthers but it was not viable, and the material was disposed of in the general waste.

A subsequent shipment of Chinese pollen by the company, seized by MAF before it was used, tested positive for Psa.

If Psa arrived in June, 2009, it was the right amount of time for symptoms to start appearing in November, 2010.

The first symptoms were found on an orchard across the road from Kiwi Pollen.

A damning report by Sapere Research last year found that MAF allowed Kiwi Pollen to import pollen from Chile and China because it was under the erroneous impression - based on flawed advice from the University of Auckland - that pollen could not transmit Psa. In fact it can.

The report found that MAF should have recognised that all imports of pollen would inevitably contain extraneous plant material. MAF knew that plant material was the prime pathway for Psa transmission and since 2004 imports of such material were required to be tested for the disease.

An exchange of emails between MAF and Kiwi Pollen shows that biosecurity was being considered, with the issue of bacteria hitching a ride on imports being discussed. Kiwi Pollen assured the department that the pollen would "always" be milled in the location it was harvested and processed there.

For the first two consignments of pollen from Chile, MAF had required the flower buds to be milled offshore, "presumably to reduce the possibility of infected flower buds being discarded", according to the Sapere report.

But the report says the wording of future import permits was changed to "may" be milled offshore.

The report described this unexplained change - which opened the way for the 2009 shipment of anthers - as "peculiar".

In a 2011 tracing report, MAF concluded that there was a low probability that pollen imports were the source of the disease.

The report said the fact the property across the road from Kiwi Pollen was the first to notice symptoms was a "coincidence" and "only a very small amount of material was imported, approximately 15 grams of pollen".

But the Sunday Star-Times has obtained a copy of the Chinese export certificate, which clearly states that it was 4.5kg of material, although it states that it was "Kiwi Pollen" rather than flowers or anthers, which may have caused confusion at the border. It is not clear who was responsible for that wording.

The Sunday Star-Times made numerous attempts to contact Kiwi Pollen, by phone, email and in person but got no response.

University of Otago biochemist Russell Poulter, whose work proved the DNA link between New Zealand's strain of Psa and China's, says anthers are tiny and there would have been at least a billion in the shipment.

"So we have a billion anthers being unpacked by Kiwi Pollen. Let's say one in a thousand carried Psa - that means you've got something like a million infective particles being unpacked by Kiwi Pollen in Te Puke."

Poulter is convinced the shipment was the pathway of Psa to New Zealand. "It's extremely difficult to prove something like that absolutely. What we are really doing is exactly the same as if it were a criminal case and you were looking at forensic DNA.

"What you do is say, ‘I have this victim and I have this DNA from the victim, and that DNA matches the accused perfectly'.

"Does that prove it was the accused? and the answer is ‘no' because it's just possible that there's someone else out there with exactly the same DNA.

"It's not absolute proof, but the balance of probabilities has shifted so heavily in favour of one possibility that it's beyond reasonable doubt."

An MPI spokesperson said the Sapere report had found shortcomings in the way MAF's systems were applied to the importation of kiwifruit material, "however, it also said that it does not automatically follow that these shortcomings contributed to the entry of Psa into the country".

MPI accepted the recommendations made in the report and had almost completed a programme of work to implement them, the spokesperson said.

They said while research done by Poulter's team in conjunction with the kiwifruit industry had indicated the local Psa strain was of Chinese origin, "there is, however, no further information on how it arrived".

And not all growers support the idea of suing MAF/MPI.

Mike Chapman, the chief executive of Kiwifruit Growers Inc, said his group had been given legal advice by a QC that any civil case would be lengthy and costly and have a low chance of success.

He did not believe there was definitive proof of how the disease got here. "You've got to prove how it got here, not just have a suspicion."

But grower Rob Thode and many others are convinced MAF is to blame. "MAF has said we will probably never know how it got here - that's their way of saying ‘you can't get us legally on negligence', but . . . we're finding more and more stuff that condemns them," Thode said.

Auckland barrister Matthew Dunning has advised the industry it has a case. "These things aren't easy. You're taking on the Government and it will be a long process, but there plainly is a complete cock-up here. We all understand biosecurity is a difficult thing to police, but you don't expect this level of incompetence to enable something like [Psa] to come in and literally destroy people's lives and waste hundreds of millions of dollars worth of value."